As in the headline. Even when setting icon size explicitly, this is ignored. The problem disappears when wrapping the QToolButton(s) in a QGroupBox, but this changes button appearance as well, so not an option.

I have attached an example project of a tool button added to the main widget and the tool bar. The difference should be clear.

Link to forum discussion about this issue: http://qt-project.org/forums/viewthread/34965/